145 research outputs found
Medium-range interactions and crossover to classical critical behavior
We study the crossover from Ising-like to classical critical behavior as a
function of the range R of interactions. The power-law dependence on R of
several critical amplitudes is calculated from renormalization theory. The
results confirm the predictions of Mon and Binder, which were obtained from
phenomenological scaling arguments. In addition, we calculate the range
dependence of several corrections to scaling. We have tested the results in
Monte Carlo simulations of two-dimensional systems with an extended range of
interaction. An efficient Monte Carlo algorithm enabled us to carry out
simulations for sufficiently large values of R, so that the theoretical
predictions could actually be observed.Comment: 16 pages RevTeX, 8 PostScript figures. Uses epsf.sty. Also available
as PostScript and PDF file at http://www.tn.tudelft.nl/tn/erikpubs.htm
Propagation of a hole on a Neel background
We analyze the motion of a single hole on a N\'eel background, neglecting
spin fluctuations. Brinkman and Rice studied this problem on a cubic lattice,
introducing the retraceable-path approximation for the hole Green's function,
exact in a one-dimensional lattice. Metzner et al. showed that the
approximationalso becomes exact in the infinite-dimensional limit. We introduce
a new approach to this problem by resumming the Nagaoka expansion of the
propagator in terms of non-retraceable skeleton-paths dressed by
retraceable-path insertions. This resummation opens the way to an almost
quantitative solution of the problemin all dimensions and, in particular sheds
new light on the question of the position of the band-edges. We studied the
motion of the hole on a double chain and a square lattice, for which deviations
from the retraceable-path approximation are expected to be most pronounced. The
density of states is mostly adequately accounted for by the
retra\-ce\-able-path approximation. Our band-edge determination points towards
an absence of band tails extending to the Nagaoka energy in the spectrums of
the double chain and the square lattice. We also evaluated the spectral density
and the self-energy, exhibiting k-dependence due to finite dimensionality. We
find good agreement with recent numerical results obtained by Sorella et al.
with the Lanczos spectra decoding method. The method we employ enables us to
identify the hole paths which are responsible for the various features present
in the density of states and the spectral density.Comment: 26 pages,Revte
Ferromagnetic phase transition in a Heisenberg fluid: Monte Carlo simulations and Fisher corrections to scaling
The magnetic phase transition in a Heisenberg fluid is studied by means of
the finite size scaling (FSS) technique. We find that even for larger systems,
considered in an ensemble with fixed density, the critical exponents show
deviations from the expected lattice values similar to those obtained
previously. This puzzle is clarified by proving the importance of the leading
correction to the scaling that appears due to Fisher renormalization with the
critical exponent equal to the absolute value of the specific heat exponent
. The appearance of such new corrections to scaling is a general
feature of systems with constraints.Comment: 12 pages, 2 figures; submitted to Phys. Rev. Let
Universality of the thermodynamic Casimir effect
Recently a nonuniversal character of the leading spatial behavior of the
thermodynamic Casimir force has been reported [X. S. Chen and V. Dohm, Phys.
Rev. E {\bf 66}, 016102 (2002)]. We reconsider the arguments leading to this
observation and show that there is no such leading nonuniversal term in systems
with short-ranged interactions if one treats properly the effects generated by
a sharp momentum cutoff in the Fourier transform of the interaction potential.
We also conclude that lattice and continuum models then produce results in
mutual agreement independent of the cutoff scheme, contrary to the
aforementioned report. All results are consistent with the {\em universal}
character of the Casimir force in systems with short-ranged interactions. The
effects due to dispersion forces are discussed for systems with periodic or
realistic boundary conditions. In contrast to systems with short-ranged
interactions, for one observes leading finite-size contributions
governed by power laws in due to the subleading long-ranged character of
the interaction, where is the finite system size and is the
correlation length.Comment: 11 pages, revtex, to appear in Phys. Rev. E 68 (2003
Reexamination of the long-range Potts model: a multicanonical approach
We investigate the critical behavior of the one-dimensional q-state Potts
model with long-range (LR) interaction , using a multicanonical
algorithm. The recursion scheme initially proposed by Berg is improved so as to
make it suitable for a large class of LR models with unequally spaced energy
levels. The choice of an efficient predictor and a reliable convergence
criterion is discussed. We obtain transition temperatures in the first-order
regime which are in far better agreement with mean-field predictions than in
previous Monte Carlo studies. By relying on the location of spinodal points and
resorting to scaling arguments, we determine the threshold value
separating the first- and second-order regimes to two-digit precision within
the range . We offer convincing numerical evidence supporting
$\sigma_c(q)Comment: 18 pages, 18 figure
Twenty Years After the Velvet Revolution: Shifts in Czech Adolescentsâ Perceptions of Family, School, and Society
Families and schools are traditionally seen as substantial socialization agents forming adolescentsâ social values and their views of society. Special attention is paid to the question whether the relative importance of these influences remains stable in times of major social changes. In this study, two different generations of Czech middle adolescents are compared: (a) the âpost-totalitarianâ generation that grew up in the last decade of the communist regime and entered adolescence during the time of rapid political and socioeconomic changes (data collected in 1995) and (b) the current generation without personal experience with the communist regime, raised in a stable democratic society (data collected in 2010). Both groups of participants (total N = 2,127, aged from 14 to 17 years) were administered an identical questionnaire. First, we examined the changes in adolescentsâ perception and evaluation of the society over the last 15 years. Todayâs adolescents perceive society more as a community and their future orientations are more focused on materialistic and less on environmental values. While the emotional relationship between the children and parentsremains the same, adolescents learn a somewhat different message in the family, emphasizing self-reliance. School environment is perceived more as positive and engaging than 15 years ago. Second, we predicted adolescentsâ social views and values from their assessment of family and school environment. Our results show that the effect of parental values on adolescentsâ value orientations is higher in the current generation. Positive school environment contributes to the development of socially responsible orientations despite the changes in society
The mediating role of self/everyday creativity and depression on the relationship between creative personality traits and problematic social media use among emerging adults
Personality is one of the important contributory factors in the development of problematic technology use. The purpose of the present study was to investigate the direct and indirect associations of creative personality traits with problematic social media use via self/everyday creativity, depression, and loneliness. A total of 460 Turkish emerging adults aged between 18 and 26 years (61% female) were surveyed. Findings indicated that (i) task-orientedness was indirectly associated with problematic social media use via self/everyday creativity, (ii) self-confidence was directly and indirectly associated with problematic social media use via self/everyday creativity and depression, (iii) risk-taking was indirectly associated with problematic social media use via depression, and (iv) self/everyday creativity and depression were directly associated with problematic social media use. The present study is the first to suggest that creative personality traits (i.e., task-orientedness, self-confidence, and risk-taking) and self/everyday creativity are associated with problematic social media use and that these factors should be taken into account when considering the etiology of problematic social media use
Preclinical pharmacokinetics and metabolism of a novel prototype DNA-PK inhibitor NU7026
In this study we investigated the in vitro time dependence of radiosensitisation, pharmacokinetics and metabolism of NU7026, a novel inhibitor of the DNA repair enzyme DNA-dependent protein kinase (DNA-PK). At a dose of 10âÎŒM, which is nontoxic to cells per se, a minimum NU7026 exposure of 4âh in combination with 3âGy radiation is required for a significant radiosensitisation effect in CH1 human ovarian cancer cells. Following intravenous administration to mice at 5âmgâkgâ1, NU7026 underwent rapid plasma clearance (0.108âlâhâ1) and this was largely attributed to extensive metabolism. Bioavailability following interperitoneal (i.p.) and p.o. administration at 20âmgâkgâ1 was 20 and 15%, respectively. Investigation of NU7026 metabolism profiles in plasma and urine indicated that the compound undergoes multiple hydroxylations. A glucuronide conjugate of a bis-hydroxylated metabolite represented the major excretion product in urine. Identification of the major oxidation site as C-2 of the morpholine ring was confirmed by the fact that the plasma clearance of NU7107 (an analogue of NU7026 methylated at C-2 and C-6 of the morpholine ring) was four-fold slower than that of NU7026. The pharmacokinetic simulations performed predict that NU7026 will have to be administered four times per day at 100âmgâkgâ1 i.p. in order to obtain the drug exposure required for radiosensitisation
Gender balance in ECEC : why is there s little progres?
Social attitudes about male participation in the upbringing of children have changed considerably over the past few decades. Men are now seen as important for childrenâs development and learning. Research from many countries worldwide shows that in early childhood care and education (ECEC), male workers are welcomed by female colleagues and parents. In the last two decades there have been initiatives for more men in ECEC in several European countries.
Nevertheless the proportion of male workers ECEC remains low worldwide. This article questions the persisting gender imbalance in ECEC and analyzes ambivalences regarding more men in the field. Based on recent gender theory, efforts and limits of strategies for more male students and workers in ECEC in Belgium, Norway and Germany are discussed. It is concluded that deeply held gendered attitudes and practices in the field of care and educational work with young children have to be put into question. More space in ECEC for embodied
subjectivities is needed to overcome essentialist conceptions of differences between body and mind, women and men
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